1. Field of the Invention:
The present invention relates to network communication techniques. More particularly, the present invention relates to a method and an apparatus for performing carrier switching in a wireless communication system using multi-carriers.
2. Description of Related Art:
“Wireless+broadband” has become a trend of network development, and various wireless communication systems are competing with each other in the field of broadband wireless access. World interoperability for Microwave Access Forum (WiMAX) is a desired broadband wireless accessing system. WiMAX is being mass tested and has been put to commercial use in countries including various European countries, America, Japan and South Korea. WiMAX is characterized by its large geographical coverage, high transmission speed, support of high speed movement, high frequency efficiency, fast deployment, low cost and so on. With pre-commercial use and commercial use of WiMAX becoming popular, WiMAX will have good development prospects.
When mobile stream media services are deployed in the future, larger amounts of traffic may be received by a Mobile Station (MS) for multicast services than for unicast services. To meet the demands for stream media services of a future market, an Enhanced Multicast Broadcast Service (E-MBS), which is similar to a Multimedia Broadcast Multicast Service (MBMS) provided by the 3rd Generation Partnership Project (3GPP) and Broadcast Multicast Service (BCMCS) provided by 3GPP2, is provided by the family of Institute of Electrical and Electronics Engineers (IEEE) 802.16 standards to support multimedia broadcast and multicast.
In addition, future services may occupy more and more bandwidth due to the increasing demand of users, and thus multi-carrier techniques are brought forward to deal with problems regarding downward compatibility, cost of a terminal, spectral efficiency and so on. Multi-carrier techniques refer to a technique which combines several carriers whose bandwidth is relatively narrow to serve one MS. The multi-carrier technique utilizes a transmitting end that should be able to transmit information to a receiving end simultaneously over multiple carriers, and utilizes a receiving end that should be able to receive information simultaneously from multiple carriers. However, it usually happens that an MS on a receiving end cannot work on multiple carriers simultaneously. Therefore the MS will have to work on at least two carriers by employing time division multiplexing. Accordingly, information transmitted by the transmitting end should not overlap with each other in the time domain. Further, sufficient time should be reserved for the receiving end to perform carrier switching and synchronization and so on, so that the receiving end can receive the information successfully. Likewise, if the transmitting end cannot work on multiple carriers simultaneously, information transmitted by the transmitting end will not overlap with each other in the time domain, and the transmitting end needs sufficient time for performing carrier switching, synchronization and transmission.
According to the current IEEE 802.16m specification, an MS receives and/or transmits information over a primary carrier, including receiving carrier switching scheduling information transmitted by a Base Station (BS). The carrier switching scheduling information includes information of at least one time slot for carrier switching. The MS then performs carrier switching according to the information of the at least one time slot, i.e., switching to a target carrier in the at least one specified time slot to receive and/or transmit information.
If the MS can only process information on one carrier at a time, when the MS needs to transmit or receive information on two or more carriers, the BS may be unable to perform the scheduling. For example, an MS has subscribed to many E-MBS services, and is receiving the E-MBS services on carrier B. If the BS is to transmit other data to the MS via carrier X, the BS has to inform the MS to switch from carrier B to carrier X in a specified time slot. In the related art, in order to support sleep mode of users and to reduce costs, the BS usually has no knowledge about which E-MBS services are being received by the MS and only has knowledge about which E-MBS services are subscribed to by the MS. Thus, the BS may regard time slots corresponding to the E-MBS services subscribed to by the MS as all unavailable for carrier switching. If the MS has subscribed to many E-MBS services, the BS may be unable to perform the carrier switching scheduling, and thus cannot transmit the needed service or data on carrier X as needed. But in fact, among the time slots corresponding to the E-MBS services subscribed to by the MS, time slots corresponding to E-MBS services which are not being received by the MS are not occupied and can be used for carrier switching.
To address the above problem, a related art solution is: in multi-carrier techniques, an MS reports a list of identities of E-MBS services being received by the MS, i.e., a list of identities and flow identities of all E-MBS services; when performing Dynamic Service Addition (DSA), the BS determines idle time slots as the time slots for carrier switching based on the list received, and includes information of the time slots in carrier switching scheduling information, and sends the carrier switching scheduling information to the MS; the MS performs carrier switching in the time slots according to the carrier switching scheduling information.
Although the above solution enables the BS to perform carrier switching scheduling for the MS, the MS is required to report the list of identities of all E-MBS services being received by the MS, and each time when there is a change in the E-MBS services being received, the MS shall report the list of identities or report information of the change, thus the signaling overhead is large. Further, the MS has to wait for a response from the BS after each report, which increases the data transmission delay and may not meet data transmission requirements of real time services in the worst situations. Therefore, when costs and complexity are taken into consideration, the above solution should be a last choice when there are other candidate solutions despite the above solution being a workable solution.